This invention relates to high-speed circuit breakers, and more particularly it is concerned with improvements in or relating to a high-speed circuit breaker of the type disclosed in Japanese Patent Laid-Open No. 92558/74.
A high-speed circuit breaker of the prior art disclosed in Japanese Patent Laid-Open No. 92558/74 comprises a pair of opposed contacts and a movable holder for supporting one of the pair of contacts. The movable holder is movable toward and away from the other contact between an ON position in which the pair of contacts are brought into engagement with each other and an OFF position in which they are disengaged from each other. A first actuator comprises a cylinder, a piston slidably received in the cylinder, an actuating rod having one end connected to the piston and the other end which is free, and a head substantially in the form of a letter L having two legs. The actuating rod is connected at the other end thereof to the end of one leg of the L-shaped head. The actuating rod is reciprocally movable axially thereof by the piston toward and away from the other contact between a first position in which the head engages the movable holder to move the latter to its ON position and a second position in which the head is disengaged from the movable holder to allow the latter to move to its OFF position.
The movable holder includes a lever having one end supporting the one contact and the other end pivotally connected to the other leg of the L-shaped head, and a pivot member having an axis extending at an angle with respect to the axis of the actuating rod including one end pivotally connected to the other end of the lever and the other end which is free. Connected to the other end of the pivot member is a pin having a roller rotatably mounted thereon and adapted to engage a supporting surface formed on the one leg of the L-shaped head. The movable head is urged by the biasing force of a release spring to move in a direction in which the lever pivotally moves about the other end thereof from the ON position toward the OFF position.
A release member has one end pivotally connected to the other leg of the L-shaped head and the other end which is free and formed with a recess and is movable between an engaging position in which the recess engages the projecting end of the pin connected to the free end of the pivot member and a disengaging position in which the recess is disengaged from the pin. A second actuator is operative, in response to an overcurrent passing through the circuit when the actuating rod of the first actuator is in the first position, to move the release member to the disengaging position to disengage the roller from the supporting surface of the one leg of the L-shaped head, to thereby allow the movable holder to be moved from the ON position to the OFF position by the biasing force of the release spring.
When the movable holder moves from the ON position to the OFF position, it is brought into abutment with a fixed abutment member, so that its movement is restricted or limited thereby.
The position in which the roller mounted at the other end of the pivot member engages the supporting surface on the one leg of the L-shaped head when the actuating rod of the first actuator is disposed in the first position and the release member is in the engaging position is located between an extension of the actuating rod and the position in which the other end of the lever is pivotally connected to the other leg of the L-shaped head. A force acting on the piston is transmitted through the actuating rod, L-shaped head, roller, pivot member and lever to the one contact, to force same against the other contact. The reaction applied by the other contact to the one contact produces a moment in the lever turning the lever in one direction about the pivot at which the pivot member is pivotally connected to the lever. Since the lever is pivotally connected to the L-shaped head, the moment acting on the lever is transmitted through the L-shaped head to the actuating rod, subjecting the actuating rod to a moment oriented in one direction. The moment oriented in one direction acting on the actuating rod tends to cause unbalanced wear on the actuating rod and the wall surface of a guide bore formed in the cylinder, giving rise to fretting corrosion.
When the actuating rod of the first actuator is in the second position and when the actuating rod is in the first position and the release member is in the disengaging position, the movable holder is urged by the biasing force of the release spring to abut against the abutment member. The lever of the movable holder is subjected to the reaction from the abutment member commensurate with the biasing force of the release spring which reaction produces in the lever a moment which tends to turn the lever in the opposite direction about the pivot at which the lever is pivotally connected to the L-shaped head. The moment acting on the lever is transmitted through the L-shaped head to the actuating rod which is subjected to a moment oriented in the opposite direction. The moment oriented in the opposite direction acting on the actuating rod tends to cause unbalanced wear on the actuating rod and the wall surface of the guide bore formed in the cylinder, giving rise to fretting corrosion.
Also while the circuit breaker is in operation, the actuating rod moves in angular movement because it is repeatedly subjected to moments oriented in opposite directions, and the sliding movement taking place between the pair of contacts increases in amount. This gives rise to the problem of misalignment of the pair of contacts.
The release spring would have the direction of its arrangement limited in such a manner that the biasing force thereof minimizes the moment oriented in the opposite direction.
An object of the invention is to provide a high-speed circuit breaker capable of minimizing the moment acting on the actuating rod of the first actuator at least when the actuating rod is in the first position and the release member is in the engaging position.
Another object is to provide a high-speed circuit breaker capable of minimizing the moment acting on the actuating rod in all operating conditions.
The first object of the invention can be accomplished by an arrangement that an extension of the axis of the actuating rod of the first actuator is disposed between the position in which the movable head engages the head and the position in which the release member is connected to the head.
The second object of the invention can be accomplished by an arrangement that an extension of the axis of the actuating rod of the first actuator is disposed between the position in which the movable holder engages the head and the position in which the release member is connected to the head and the lever of the movable holder is connected to a stationary frame.